Low observable, or stealth, technology is utilized on aircrafts, ships, submarines, and missiles, for example, to make them less visible or observable to radar, infrared, sonar and other detection methods. Various radar absorbing materials (RAMs), which absorb electromagnetic frequencies, such as in the radar range, have been developed for such low observable applications. However, the RAMs presently employed have some drawbacks. For example, many RAMs are not an integral part of the surface of a low observable structure. Instead, the RAMs are applied as coatings or paints over the surface of the low observable structure making them heavier, and prone to wear, chipping, and failure. An example of such a RAM includes iron ball paint, which contains tiny spheres coated with carbonyl iron or ferrite. Moreover, these coatings require bonding to the surface of the structure because they are not an integrated part of the structure or surface.
Another example of a RAM is urethane foam impregnated with carbon. Such RAMs are used in very thick layers. Such RAMs are inherently non-structural in nature such that they add weight and volume to structures while providing no structural support. These types of foam RAMs are frequently cut into long pyramids. For low frequency damping, the distance from base to tip of the pyramid structure is often 24 inches, while high frequency panels can be as short as 3-4 inches.
Another RAM takes the form of doped polymer tiles bonded to the surface of the low observable structure. Such tiles which include neoprene doped with carbon black or iron particles, for example, are prone to separation, particularly in extreme operating environments such as extremely high or low temperatures, and/or high altitudes. Finally, numerous RAMs do not perform adequately in the long radar wavelength band, about 2 GHz.
It would be beneficial to develop alternative RAMs that address one or more of the aforementioned issues. The present invention satisfies this need and provides related advantages as well.